Solar Heating, Energy Efficiency, MEP, Indoor Air Quality, Carbon, Greenhouse Gas, GHG, IAQ, HVAC, COVID-19
With the COVID-19 pandemic, the paradigm is shifting for ventilation air.Given its attention in mainstream media, political rhetoric, industry guidance and changing regulations, the focus on ventilation air has never been more prominent than it is now. For years, buildings have reduced their fresh air intake to help minimize energy consumption (and corresponding carbon emissions) and achieve better performance standards. This strategy, however, is now being challenged by the need to dramatically increase fresh air intake to improve indoor air quality (IAQ) and minimize the risk of indoor airborne transmission of the novel coronavirus.
This is an important discussion for consulting engineers and building designers to contemplate nowâ€”and there are ways to increase ventilation air intake without incurring a corresponding increase in energy costs and carbon emissions. One such option is the use of solar air heating.
No need for a trade-off
One example of this technology is the use of a perforated metal collector system to preheat ventilation air before it enters the fresh air side of a buildingâ€™s HVAC unit. These systems can be mounted on a buildingâ€™s wall or roof, sized to accommodate anywhere from 1 to 10 cfm of ventilation air per sf.
This technology has already been used extensively across North America over the past 30 years for many types of buildings, including schools, universities and colleges, and has allowed them to meet or exceed their required ventilation intake without increasing energy costs. Thus, there is no need for an energy efficiency trade-off when tacking the problem of COVID-19.
One of the prominent industry advocates in the media has been William P. Bahnfleth, professor of architectural engineering at Penn State University and chair of ASHRAEâ€™s Epidemic Task Force.
â€śThe U.S. Centers for Disease Control and Prevention (CDC) have stated airborne transmission of SARS CoV-2 can occur when there is inadequate ventilation indoors,â€ť he explains. â€śThis is corroborated by evidence from superspreader events. Multiple analyses of infection risk have concluded the combined effect of ventilation, filtration and air cleaners should be equivalent to four to six air changes per hour of outdoor air, although there is considerable uncertainty associated with these estimates. HVAC systems should be inspected to confirm they are bringing in at least the outdoor air supply required by a minimum design standard, such as ASHRAE 62.1.â€ť
ASHRAE also released a position document on infectious aerosols, including the following recommendations:
Disable demand-controlled ventilation and open outdoor air dampers up to 100%, as conditions permit, to eliminate recirculation.
Keep HVAC systems running longer hoursâ€”if possible, 24-7.
Bypass energy recovery ventilation systems that leak potentially contaminated exhaust air into the outdoor air supply.
Solar air heating systems are ideally suited to help meet all of these recommendations, as there are numerous ways to incorporate them into buildingsâ€™ mechanical ventilation systems.
â€śWe have successfully incorporated solar air heating for multiple secondary school projects, including both new construction and upgrades,â€ť says Robert Cenedese, principal at Rocky Point Engineering in Langley, B.C. â€śThe original design intent of preheating demand-controlled ventilation air has proven to work effectively. Interestingly, an additional feature has been implemented through direct digital control (DDC) programming. When conditions permit, preheated solar air is used as first-stage heating for the spaces served, regardless of carbon dioxide (CO2) demand. Thereby, in addition to heating the spaces using free solar energy, the ventilation airflow rate increased, resulting in improved IAQ without increased energy consumption or carbon emissions. A true win-win!â€ť
Case in point
Fanshawe College in London, Ont., is an example of a large campus that has implemented a greenhouse gas (GHG) reduction road map and action plan to ensure low-carbon buildings. The process included an ASHRAE Level 1 energy audit, with the goal of reducing GHG emissions by 30% between 2013 and 2030â€”and 50% by 2050.
The college found ventilation air heating was a significant contributor to its GHG emissions, due to the consumption of natural gas as a source of heat energy.